1. Field of the Invention
A device, such as a flexible spinal fusion cage, which can articulate (bend) in such a way that it will be able to be implanted from a lateral approach into L4-L5 and L5-S1 is disclosed.
2. Description of the Related Art
Typical lateral approach fusion implants (e.g., Discover XLIF, by NuVasive, Inc., San Diego, Calif.; and the Direct Lateral Interbody Fusion (DLIF) by Medtronic, Inc., Minneapolis, Minn.) are not able to implant their fusion cages for two reasons.
First, boney obstacles can impair access. FIGS. 1a and 1b illustrate the pelvis and lower spine including the Ilium 2, sacrum S1, and lower lumbar vertebrae L3, L4 and L5. FIGS. 1a and 1b show the challenge of gaining lateral access to the L4-L5 and the L5-S1 intervertebral spaces. The position of the Ilium 2 obstructs the direct lateral access pathway.
FIG. 2 illustrates windows 4a and 4b or channels which some doctors create during implantation. The windows 4a and 4b are created through the Ilium to gain direct line of site access to the L4-L5 and L5-S1 intervertebral spaces, respectively. This is a highly invasive approach, creates significant tissue damage, particularly to the Ilium and surrounding soft tissue, and requires significant surgical skill.
Second, the steep approach angle (8a for the L4-L5 intervertebral space and 8b for the L5-S1 intervertebral space), as measured from a transverse plane along the approach path (10a for the L4-L5 intervertebral space and 10b for the L5-S1 intervertebral space) of a tissue retractor relative to the location of the fusion site, can cause problems, as illustrated in FIGS. 3 and 4. The approach paths 10a and 10b pass through the skin surface 12. The tissue retractor used in lateral fusion surgery provides line of site access to the disk space requiring a fusion cage insertion. The tissue retractor holds tissue out of the way of the procedure. The tissue retractor is also used to create a working channel to pass tools through, protect neural tissue, and anchor to the superior and inferior vertebral bodies relative the disk space requiring fusion. The volume within the pelvis and inferior to the dashed demarcation line 6 along a transverse plane is very hard if not impossible to reach with a direct lateral approach due to the Ilium. Even if the retractors are tilted as shown by the demarcation line 6, the ability to insert an implant that is the length of the end plates of the L4 or L5 vertebral bodies would be very difficult due to obstruction of the Ilium among other factors.
Furthermore, with the retractor positioned along the approach path 10a or 10b plane and angled direction, the angle formed between the retractor and the vertebral body end plates would make inserting a monolithic, inflexible fusion cage 14 or implant into the L5-S1 intervertebral space difficult if not virtually impossible due to obstruction of the surrounding hard and soft tissue, as illustrated by FIG. 5a. A typical lateral fusion cage or implant width 16 is the width of the end plate 18 along the adjacent disk. The implant 14 can not turn the corner at the pivot point 20 at the lateral and/or anterior edge of the L5-S1 intervertebral space.